Shear strengthening of continuous concrete beams using externally prestressed steel bars

This study focuses on the shear behavior of continuous reinforced concrete beams strengthened with externally prestressed steel bars. Three 3-span beams were tested to failure in shear. One conventionally reinforced beam without external steel bars was used as the control, and the other two beams were strengthened with external steel bars of 18 or 22 mm (0.71 or 0.87 in.) diameter. The external steel bars were installed only on the interior span and had a deviator (or saddle pin) at midspan. The shear span-to-depth ratio was 4.6. The target effective prestress was 25% of the measured yield strength of external steel bars. Test results show that the load-carrying capacity of two strengthened beams with externally prestressed steel bars was increased by about 35% over the reference beam and that their serviceability characteristics (uncracked stiffness and recovering of deflection) were greatly improved. In addition, the measured shear strength was compared with the strength predicted by ACI 318-11 and AASHTO LRFD specifications for prestressed concrete beams. Both the ACI 318-11 detailed approach and AASHTO LRFD specifications method predicted the measured shear strength and failure location of the tested continuous beams with external bars quite accurately.